The CP is that the universe is homogenous in every direction and there's no privileged point. Any extremely large structure would violate that principle because it's clearly different than the rest of the universe

On the humongous scale of the unverse, imagine the galaxies spread out like static on a mistuned TV. Pick a spot, how would you explain to another person, relative to the features on the image, where that spot is? It would be impossible, however if there's a cluster of white dots (galaxies) around the lower left corner, you could describe the spot's location relative to that location.

I've read a few articles saying the size is so large that it shouldn't even exist.. Why is that? We know the universe is billions of light years across (I used billions just as an example.. It could be never ending) so wouldn't one assume that they're could be an object of that size out there?

The structure in the universe is, according to the Big Bang-inflationary cosmology, a result of quantum fluctuations in the hyper-early universe (think when the universe was less than 10-36 seconds old) which got blown up to much bigger size during a period known as inflation. We do not expect these structures to get larger than a certain size, because even as matter is clumping up, the universe is expanding and making it harder for very large structures to form.

If this discovery holds up (I admit I'm a wee bit skeptical, but I still need to read the paper) it would indicate that there's something we don't understand about large-scale structure formation in the universe.

Don't laugh or make fun, but is there any way you could ELI5 that for me? I'm always on that subreddit and was told to check out r/askscience but I'm not a scientist or anything. Just someone who is in love with learning and in love with space and astronomy, abiogenesis, etc.

Imagine you're dumping a big bag of marbles across a smooth floor. You'd expect them to scatter in every direction. Some will bump into each other and make little clumps, which would be normal, but for the most part they'll be pretty well spread out.

The LQG, according to some sources, seems to be a massive clump of marbles - so big that it doesn't quite make sense, if we are to assume they were dropped in the way we believe they are. So either Einstein's Marbleogical Principle is in question (less likely) or we don't have a complete understanding of the LQG (more likely).

But even if the chances are minimal, couldn't a bunch of marbles go to the same direction? If the universe is infinite, aren't also the probabilities that this could happen? I have a theory but I'm not a scientist and it might sound terribly.stupid.

That argument applies better to things that we don't have any actual evidence for - i.e. even in an infinite universe, a non-zero probability of something does not necessarily translate to its existence. But in this case, we have evidence for a phenomenon, and if our theories say that it could happen, finding that it has happened is not such a problem in principle.

It's not a problem in principle, but impacts our bayesian inference about the theory.

The relative likelihood of the theory has gone down. Instead of "The theory is true" vs. "the theory is false," we have "the theory is true AND something very improbable happened" vs. "the theory is false."

The question was: given an infinite universe, isn't the probability of event x happening "infinite"?

There were two parts to the question. The answer to the first part, "But even if the chances are minimal, couldn't a bunch of marbles go to the same direction?" is yes.

By which I assume he means "Isn't the probability 1?". The answer, no matter how you look at it, is "no".

Yes, that's what I was saying when I wrote "even in an infinite universe, a non-zero probability of something does not necessarily translate to its existence." But even though the answer to this part of the question is no (given our knowledge of the nature of the universe), it doesn't affect the answer to the first part.

The example above doesn't take into things like gravity and quantum effects. For example, multiple marbles will not exert significant gravity on each other, right? This expanding big-bang matter would. However, this would logically point to LARGER clusters of "marbles", not smaller, so the last trick is how much energy this matter has / how fast your marbles are moving. In this case, your marbles are not really just a handful being dropped, it's more like multiple tons being shot out of machine guns.

And my understanding is that yes, there would be some probability that clumps could form, but imagine how insanely small that is. We would say that an event like this "could not occur" in the same way that, when trying to catch a baseball, it wouldn't pass through your hand. According to quantum laws, there is actually some 10-10-10-10 or something chance that your baseball could be observed on the other side of your hand, but it won't ever actually happen. My understanding is that the same thing is occurring here.

This is actually one criticism of the paper. What the authors observe is unlikely by chance. Nevertheless, there's a small chance that random variation will produce something that looks like a large structure. If you look in enough places, it's actually not that surprising that you'd find something unusual.

In other words, some people still doubt that the observation is statistically significant.

It simply being large isn't the root of the problem. Current cosmology sets a limit on how large structures should be based on the speed of gravity propagation and the inflation of the early universe. The current "calculated" size of the universe is infinite, so no, it's probably not larger than infinite.

I'm not a physicist so i'm just trying to understand this from a mathematical view point. Your analogy seems to imply that one can think of CP as saying that the distribution of matter in the universe follows a uniform distribution (or some distribution along these lines). And that the discovered quasar represents a sample of points that are so clustered so that if we were to try to test the hypothesis that universe is homogeneous, it would fail because of this quasar. Have i abstracted this correctly in terms of the mathematics?

Yes, but I would be careful to note that only this one test has "failed," not the entire hypothesis. It may be more appropriate to view this from a bayesian perspective.

Say there is a set of all hypotheses Hn about how matter is distributed in the universe, and a level of belief or probability in each hypothesis P(Hn). Each hypotheses has a corresponding probability P(Cluster|Hn) that a cluster this size could exist within our observable universe.

You can use those probabilities to apply a bayesian update/inference based on the observed cluster, and those hypotheses that found the cluster unlikely are now relatively less likely to be true than they were before. But if the prior level of belief in Einstein's theory was very high based on previous experiments, it would still be the most likely explanation.

Based on the basic idea of dropping marbles on the floor, wouldn't there still be a small chance of a clump that is unexpectedly large, like this group of quasars? If not, is that just where the analogy happens to end?

Why is Einstein unlikely to be wrong? I don't understand how we can be so cocksure about the behaviour of matter at times close to the big bang. We're sure about the marbles because countless experiments have verified classical laws of mechanics that describe these marbles nicely.

How stuff 'flies' after the Big Bang? We have no idea. Just theories. And equations.

Well...yes and no. You're right that when we talk about the enormous structure of cosmic things or times close to the big bang, we can't (currently) directly measure what's happening so we rely on theoretical models (General Relativity and the Standard Model) to shine some light on the topic.

But, the thing about these models is that describe lots of stuff that we can directly measure. And, measurements we have made. Stacks, nay, mountains of measurements that we compare to what our models say. That way we get an idea how accurate the model is or if it's garbage.

And every measurement we make, every test we throw at these models (GR and SM) only backup/confirm what they say.
They're very good.

So, when something shows up that says our models are wrong, that could well be the case. But, their track records are so good that we're justified being confident they aren't.

There is a lot more information in photons than you let on. You're also over simplifying it.

Our understanding of the universe is very grand, however, imperfect. We point telescopes at fuzzy patches and make statements like "well this group of quasars doesn't agree with what we thought we knew about the universe, let's change our previous statements about the universe to align with new observations"

Einstein is unlikely to be wrong because there is overwhelming evidence that the universe started out isotropic and homogeneous, so it's doubtful that it currently is not isotropic and homogeneous.

Meh. My experience with working in a lab leads me to take nothing based on theory and everything on verifiable testable things I can hold in my hand. I'd say overwhelming evidence would be seeing it. Or something.

And what always strikes me is what...was going on before that? Why was everything very hot and massive? Was the mass arbitrary?

In short, loads of questions, and meaningless statements like "Lets make time and space one continuum" instead of answers.

This is one of those times when our fellow scientists somewhat annoy me. Let's take our observation, confirm it, and revise our theory - not make a big fuss about it and try to force a square peg into a round hole. A uniform universe is an idealized model. Sometimes hypotheses are wrong, and when it comes to understanding the universe on the macro-scale, I'd expect us to be wrong quite often.

EDIT: I got so caught up in my anger that I forgot to commend you on the analogy. Great example.

In a way, there are divots in the floor and those divots are dark matter. Without dark matter there would not be enough gravity to hold galaxies together and they would never form. To use your analogy the divots are spread uniformly throught the whole area of the floor so that there is still a uniform distribution of marbles. The discovery of the LQG is more like a pothole in the corner than a divot so there is a greater concentration of matter there than anywhere else.

This is the first direct observable evidence that goes against the cosmological principle so it is potentially a very interesting and very groundbreaking discovery (again, the cosmological principle states that on large scales the universe is homogenous and isotropic, ie. there is no preferred direction to point your telescope and there is no preferred position for your telescope...the universe looks the same in all directions).

One of the big questions that this raises is how did it form in the first place? In the early universe such a concentration of matter should have probably formed a black hole, yet it didn't. As AArondhp24 pointed out, if the universe is expanding uniformly then the structure should have drifted apart as the distance between the quasars grew larger, yet it didn't.

The discovery of the LQG is more like a pothole in the corner than a divot so there is a greater concentration of matter there than anywhere else.

Who says there aren't others like this one yet to be discovered? :)

(again, the cosmological principle states that on large scales the universe is homogenous and isotropic, ie. there is no preferred direction to point your telescope and there is no preferred position for your telescope...the universe looks the same in all directions)

Einstein was generally iffy on this idea, and I was never one to completely buy into it. I feel like we know so little about macro-scale structure that the topic really just needs to wait for further observations. Findings like this one may prove this "idealized" vision of the universe incorrect.

As AArondhp24 pointed out, if the universe is expanding uniformly then the structure should have drifted apart as the distance between the quasars grew larger, yet it didn't.

Unless the gravitational binding energy was so concentrated and uniform that the dark matter halo that gathered around the quasar mass almost "isolated" it from the rest of space - expanding space beyond the typical realm of the CC beyond the perimeter of the system, while at the same time keeping the interior relatively uniform. It really boils down to the great question: what the heck is dark matter? Not the effects of it, but exactly what it is. We're at the point now where it is becoming a crucial question to answer in furthering our understanding.

But if the gravitational binding energy was so strong then why didn't it all collapse into a primordial black hole? For such a structure to be visible today it would have had to be a lot more tightly packed in the early universe.
I wonder though if all it took to create this structure was a slight inhomogeneous distribution of dark matter after the big bang, causing a cascading effect of normal matter concentration as the universe aged.

Would it be possible for a larger amount of the marbles in that area to be stickier than normal? (i.e. black holes being more prevalent allowing for greater attraction due to the increase of gravity caused by said black holes?)

At the start of the universe, the universe was extremely, extremely dense, and it was also very smooth-- there was little or no difference in density between two different places in the universe. However, when you look at how the universe behaves on very very tiny scales, there are quantum fluctuations or irregularities which would make a smooth matter distribution (as we have in the early universe) become a bit bumpy. Some regions become a tiny bit denser than others.

Then, suddenly, for reasons that we still don't really understand, the universe INFLATES!1 A region which before inflation was the size of an atom become larger than a solar system, all in a tiny tiny fraction of a second. Now, those tiny bumps and irregularities we were talking about, they get expanded too-- so instead of being tiny and microscopic, they're larger in size.

After inflation, the universe continues expanding, and these bumps start growing and pulling in more matter. If the universe hadn't undergone inflation, then it would have taken much longer for the bumps to get to that size, and in that time they could have grown even more than they did. So inflation keeps the universe's matter distribution a lot smoother than it would be otherwise. This is one of the big reasons why inflation is considered accurate by most cosmologists, because it's the only known way to explain why the universe is so smooth.

Because of this process of inflation, there's a limit to how large these bumps can grow. We expect the universe to be pretty smooth on scales larger than several hundred million light years, but this structure is apparently a couple billion light years across. So either the discovery is erroneous, or something we thought we knew is not actually true.

Awesome explanation. This may be helpful with the parantheses quoting issue. Reddit's syntax works a bit like regular expressions in Unix, you can "break" the second parenthese by putting a \ in front of it. This tells the parser to treat it literally. Hope this is helpful.

Is it possible/how likely is it that our knowledge of the size of the universe is wrong? Also, perhaps how old the universe is?

We can only estimate the size of the observable universe; the universe as a whole is generally surmised to be infinite. Our estimates of the universe's age are very accurate (for cosmology)-- it's 13.7 billion years old, with a margin of error of at most a couple hundred million years (i.e., a couple percent). There are several lines of evidence which all agree pretty strongly with this, the most notable being the Cosmic Microwave Background, which gives us a picture of the universe as it was 400,000 years after the Big Bang. The well-constrained age means that the light from the CMB has traveled 13.7 billion lightyears to get to us, although the matter which emitted it is now much more distant than that.

When you say "which gives us a picture of the universe as it was 400,000 years after the Big Bang," what type of picture are you talking about? Is this just saying they "know" what it should have looked like, or is there a way to make an actual image using the data?

A very literal picture. At that time, the universe became transparent enough that all the photons which had previously been coupled with the dense plasma were able to stream freely in all directions. We can directly detect those photons, which have been traveling for 13.7 billion years. Satellites such as COBE, WMAP, and now Planck have measured the size and magnitude of the variations in the background to infer a great deal about the properties of structure in the universe.

Note: the above image severely exaggerates the anisotropies (i.e. bumpiness). The CMB is actually smooth to within a thousandth of one percent.

there are quantum fluctuations or irregularities which would make a smooth matter distribution (as we have in the early universe) become a bit bumpy.

Could the large scale object be a result of quantum fluctuations preserving symmetry so even though they are bumpy they must have held some sort of symmetry, or did quantum mechanics not work like that in the early universe/now?

Could the large scale object be a result of quantum fluctuations preserving symmetry so even though they are bumpy they must have held some sort of symmetry, or did quantum mechanics not work like that in the early universe/now?

Thank you! I read and understood that so much easier! Lol. Another question... Life as we know it and space and stars/galaxies/solar systems/etc was all in a space the size of an atom at Big Bang? So, what was that "atom sized space" sitting in? When it exploded and started expanding, what was it expanding into? When all that was in such a tiny tiny space, there had to be something around it and away from it, right? And what caused it to start expanding to begin with? Just got to a certain temp or ??

We do not expect these structures to get larger than a certain size, because even as matter is clumping up, the universe is expanding and making it harder for very large structures to form.

We don't expect thing to be bigger than a certain size because as the Universe expands (uniformly we think) there will not be enough matter in one space that could create something so large.
It's like trying to make a snowball out of frost on the grass. There's LOTS of frost, but not enough in one spot to make a decent sized snowball.
Basically the universe spit out a snowmans head, and we're left to wonder "How is that possible?"
This could be our centuries "The Earth is not flat" moment.

Does it have anything to do with the speed that gravity has an effect an object? Doesn't this structure challenge the theory that the effective speed gravity travels at is the speed of light?...meaning not enough time has passed in the observable universe for something so large to be bound together by gravity. I may be entirely wrong.

Hmm, I'm learning all kinds of things from this thread. Seems the consensus is that the universe is considered to be infinite.

The observable universe is still !@#$ing huge though. Yes, there's more, because we haven't seen it all and we know that. I guess the answer to your question is yes, we are not looking at the universe on a large enough scale. But we "know what we don't know" in a lot of senses (though certainly not all), and we're exploring.

Really, that's all it takes? I mean just thinking about Poisson's and Bayes' works, it's fairly commonplace that "randomness" in nature occurs in clusters. For instance, there's a reason why coin tosses don't just always end up alternating between heads and tales with every flip... you might have trains of up to 10 flips where you get all heads, for instance, even though the probability is theoretically 1/2 of for getting either.

But that's exactly it - it's not strange to think of some random clusters showing up on a small scale, like getting 10 or 20 heads in a row. But if you flip a coin a million times it should be very very close to random chance. So with this new LQG observed on such a large scale it's like flipping a coin a million times and getting 60% heads. It's not physically impossible, but one would assume there is some extra unknown force acting upon it, as opposed to the incredibly small chance of this happening randomly.

Why would we expect the universe to be homogenous? Would there not have been a "ground zero" for the big bang and everything would be flung outward from there. Why would there not be nothing in the middle and a shell of matter expanding outwards like a shockwave?

It's strange to think about, but it's because the universe is expanding into the fourth spacial dimension. A good analogy is picturing the two dimensional surface of a balloon. The surface of an expanding balloon is our universe, but as the surface (or material) of the balloon gets bigger it expands into the third dimension: so no part of the surface (which would be our universe) would be considered a "center" relative to any other part.

In that image I see several line segments of galaxies going from southwest to northeast aligned in parallel that stand out from the rest of the noise. Does that mean anything or is that just an artifact of the image?

This a bit of a different question: if this LQG is 4 billion light years across, how much of it is actually quasars? Is it just a region of space that has something like 5% more average-quasar-per-volume than other regions of space, or is it an actual clump of quasar, like a galaxy cluster but larger?

I mean, with a size that large there aren't just trillions upon trillions of quasars just sitting there, right?

From reading the article (whose link fredrol so kindly provided below), it appears that it's a ~40% overdensity. There's still plenty of space between the quasars, and they're not gravitationally bound in the same way that a galaxy or galaxy cluster is.

I don't see this in here, so if someone could also help me understand: how did we not see this thing before? What was preventing its detection previously? I only know enough astronomy to know how little I know, so I appreciate the help.

But wouldn't you expect to find some outliers in such a large sample? I mean, each time you flip a coin it has a 50% chance of heads or tails, but you would expect a run of maybe 10 or 15 heads or tails in a row, given a large enough data set.

That's what I was thinking, but perhaps this is like a clump that would require you flip heads a thousand times in a row or something? If somebody could explain it in more detail that would be great. How unlikely is it that something like this could occur normally?

I may not understand fully, but considering how far back in time you are looking to observe this and given the smaller size of the universe back then, wouldn't it make sense for structures to be closer together as they haven't spread out yet? Or even that such a structure doesn't exist now due to its huge size and has broken up or collapsed already

When Einstein used the Copernican Principle for the first time, he postulated that no average property of the cosmic medium defines a preferred place or preferred direction in space. He assumed, in fact, that all the observers connected with the typical particles of the Universe are equivalent to each other. This formulation of the principle was sometimes called the Cosmological Principle of Einstein. Milne (1935b) was of the opinion that this principle is more general than the theory of General Relativity, which is just one of a number of its possible realizations. However, in fact, it proved not to be so. The theory of General Relativity can be applied to cosmology without acceptance of this principle (cf. 4.07). The form of the Copernican Principle used by Einstein can also be helpful today for understanding some properties of the Universe. But the name the Cosmological Principle of Einstein is rather seldom used.

No. The last sentence in the quote says "...the name the Cosmological Principle of Einstein is rather seldom used." Not only that, but if you notice in the description, this is not a principle that Einstein formulated wholly on his own. Instead, he used the Copernican Principle (according to the description) and incorporated additional details about what he believed to be a universe which is homogeneous.

If Einstein had found a cosmological principle all his own then it would 'count' as being truly his.

Have they completely ruled out that this isn't just some strange coincidence? Assuming the universe is relatively uniform and quasars occur randomly (independently), then they should follow a poisson distribution and given significantly large numbers a random universe would almost certainly have anomalies like this. What am I missing here?

Who cares if it threatens a principle or law? This is science, we strive for the unknown and impossibilities. At least we should be. Every day we get new information, new data, a whole new world essentially. Making yesterday seem barbaric in comparison.

I cant add much more since I am an undergrad chem student.

Edit: I am not saying that we should ignore everything, but we should accept change and understanding more readily. When there is a fact, we should accept it because nothing will change that fact at that point in time.

It's not that the scientists here are 'closed-minded' in any way, it's that some of us here are astounded that something like this exists. After all, it's a cluster 4-billion LY wide! That's HUGE. Assuming this finding holds up, it means we'll have to revise how we view the large-scale structure of the universe.

Also, it's not guaranteed that this finding is fact yet. This finding is anomalous. Since it goes against what we already know about the large-scale structure of the universe (and inferred homogeneity), the data has to be reviewed, images studied, and more observations need to be made to verify that this is true.

If we only ever observed anomaly once then called it fact, than at this point we'd already be looking for ways to travel faster than light (due to the first observations of that neutrino moving 'faster than light' --this was later found to be due to a mechanical malfunction in the timing apparatus of the collider). This finding had the potential to go against everything we know, but it turned out to be nothing, through systematic re-observation and verification of results.